Diving with diabetes: what's allowed, what's not, what to plan

The honest TL;DR

For most of scuba history, diabetes was an automatic medical disqualification. The fear was reasonable: hypoglycemia underwater causes confusion, loss of coordination, and unconsciousness — at depth, those translate to drowning. Insulin pumps weren’t designed for water pressure. Continuous glucose monitors didn’t exist. The default was “no.”

That changed in 2005, when the Divers Alert Network (DAN) and the Undersea and Hyperbaric Medical Society (UHMS) co-hosted a consensus workshop that produced the Guidelines for Recreational Diving with Diabetes. Those guidelines, refined by SPUMS (the South Pacific Underwater Medicine Society) and adopted broadly by dive medicine worldwide, are the framework every reputable dive doctor uses today.

The short version: diabetes is no longer a blanket disqualifier. It is a conditional permission, granted to divers who meet specific medical criteria and follow specific glucose protocols on every dive.

Why diabetes matters underwater specifically

A hypoglycemic episode on land is unpleasant but rarely fatal. You feel shaky, you eat something, you recover. Diving removes nearly every part of that recovery loop.

• You cannot recognise symptoms reliably at depth. Nitrogen narcosis, cold, exertion, and stress all mask early hypoglycemia signs. By the time you notice, you may already be impaired.
• You cannot eat underwater. Standard rescue protocol — fast-acting carbs by mouth — is impossible at 18 metres. Glucose gel in a BCD pocket helps only if you can get it out, into your mouth, and swallow it without removing your regulator. Doable but slow.
• Exertion swings blood glucose unpredictably. Finning against current, dragging gear up a ladder, fighting a tangled SMB line — all spike adrenaline and consume glucose at rates you don’t experience on the surface. Surface intervals don’t always restore baseline.
• Cold water increases glucose consumption. A 24°C tropical dive is metabolically different from a 12°C UK dive. Both burn glucose, but the cold dive burns more.
• Stress responses can mask or mimic hypoglycemia. Mild anxiety on a deep dive feels uncannily similar to a low. The diabetic diver has to interpret signals that healthy divers don’t even have to think about.

Hyperglycemia is also relevant but less acutely dangerous in a single dive. The bigger long-term issue is that chronic high blood sugar causes the complications (retinopathy, neuropathy, kidney disease) that themselves disqualify diving.

The 2005 DAN/UHMS consensus — what it actually says

The workshop brought together endocrinologists, dive physicians, and diabetic divers who had been diving (sometimes covertly) for years. The output was the first widely-accepted protocol for medically clearing diabetics to dive.

Core requirements from the consensus, paraphrased:

The full set of requirements typically applied by dive-trained physicians in 2026:

• Diabetic stability for at least one year (Type 1) or three months (Type 2) on the current treatment regime
• HbA1c below 9% as an absolute floor, with most dive doctors preferring under 7%
• No episodes of severe hypoglycemia (requiring third-party assistance) in the last 12 months
• Intact awareness of hypoglycemia — the diver must reliably feel a low coming on
• No significant diabetic complications: no proliferative retinopathy, no autonomic neuropathy, no significant nephropathy, no peripheral vascular disease affecting circulation
• No diabetic ketoacidosis (DKA) episode in the last 12 months
• An annual review with the dive physician, with HbA1c re-checked

These thresholds aren’t punitive. They map directly to the failure modes — recent severe hypos predict future severe hypos, complications predict that something else will go wrong at depth, unstable HbA1c predicts unpredictable glucose response.

What you actually do on a dive day

The medical clearance is the entry ticket. The everyday protocol is what keeps you safe. Most dive-medicine-trained physicians will hand you something like this.

The 150/300 protocol — the de facto standard:

• Check blood glucose 60 minutes, 30 minutes, and immediately before each dive
• Pre-dive target: 150–300 mg/dL (8.3–16.7 mmol/L)
• Below 150 mg/dL pre-dive: eat fast-acting carbs, recheck in 15 minutes, do not dive until stable in range
• Above 300 mg/dL pre-dive: do not dive — risk of ketosis and dehydration is too high
• Trend matters: if glucose is 160 mg/dL but falling fast, treat it as low

On the dive:

• Carry fast-acting glucose (gel, tablets, or a sugary drink in a pouch) reachable without removing your regulator
• Brief your buddy on the universal hypoglycemia signal — most divers use the “L” hand sign on the chest or thigh
• If you feel a low coming on, signal, ascend together, deploy glucose, surface if needed
• Never push through “I’ll be fine for another five minutes” at depth — that’s the thinking that gets diabetic divers killed

Post-dive:

• Check glucose immediately on exit, then again 15 and 60 minutes later
• Post-dive lows are common — exertion and the dive itself continue burning glucose for hours
• Eat a slow-carb snack on the boat regardless of reading
• Long surface intervals (60+ minutes) between dives, not 20

On insulin pumps and CGMs: most pumps and continuous glucose monitors are not pressure-rated for recreational depths. Standard practice is to disconnect the pump before the dive (with appropriate basal compensation) and reconnect on the surface. Some divers leave CGM sensors in place — manufacturer guidance varies, and the sensor reading is often unreliable at depth. Check your specific device’s spec sheet and ask your endocrinologist, not the dive instructor.

Type 1 vs Type 2 — different problems, similar protocol

The clinical reality is that Type 1 diabetics are the higher-risk group for diving because:

• Insulin is exogenous and can’t be turned off mid-dive
• Glucose swings are typically faster and larger
• The risk of severe hypoglycemia is structurally higher

Type 2 diabetics on diet, metformin, or non-insulin medications (GLP-1 agonists, SGLT-2 inhibitors) generally have a lower hypoglycemia risk and are easier to clear. Type 2 diabetics on sulfonylureas or insulin are treated more like Type 1 for diving purposes — the medication, not the diagnosis, drives the hypoglycemia risk.

A subtle but important point: GLP-1 agonists (Ozempic, Wegovy, Mounjaro) and SGLT-2 inhibitors (Jardiance, Forxiga) have specific diving considerations. SGLT-2s especially have been associated with euglycemic DKA — ketoacidosis at normal blood sugar — which can be triggered by dehydration and exertion. Some dive physicians ask SGLT-2 users to pause the medication on dive days. This is an endocrinologist-and-dive-doctor conversation, not something to figure out yourself.

What to bring on the boat

A diabetic diver’s kit list is non-trivial. Plan it once, then it’s routine.

• Glucose meter + spare batteries + spare test strips (sealed)
• 3–5 fast-acting glucose sources (tabs, gel, or sugary drink) — more than you think you need
• Slow-carb snacks for the surface interval (bananas, peanut butter sandwiches, energy bars)
• Insulin (if you’re on it) in a temperature-stable container — boat sun gets brutal
• Glucagon emergency injection (the dive boat staff should know where it is)
• Spare pump supplies if you’re a pump user
• Written hypoglycemia treatment plan in your dry bag — for the boat crew if you can’t communicate
• Medical ID bracelet or dog tag stating “Type 1 diabetic” or equivalent

Brief the boat captain, divemaster, and your buddy at the start of the day. Not in a way that makes a scene — just “I’m a Type 1 diabetic, here’s where my glucose is, the signal is X, here’s my glucagon if I’m unconscious.” Reputable dive operators handle this calmly because they’ve seen it before.

When diabetes still disqualifies

The 2005 consensus opened the door, but not for everyone. These are the conditions where most dive physicians will not clear a diabetic for recreational diving:

• Severe hypoglycemia requiring assistance in the last 12 months
• “Brittle” diabetes with frequent, unpredictable glucose swings
• DKA episode in the last 12 months
• Hypoglycemia unawareness (you don’t feel lows coming on)
• Proliferative retinopathy — the pressure changes from descent can worsen it
• Significant autonomic neuropathy — your heart-rate and blood-pressure responses to stress are blunted
• Symptomatic coronary artery disease — diving is a cardiovascular stress test
• Pregnancy with diabetes — diving in pregnancy is contraindicated regardless of diabetes status

This list isn’t gatekeeping. Every item on it predicts a meaningful underwater failure mode.

Finding a dive-trained physician

A regular GP cannot clear you to dive with diabetes. Even most endocrinologists can’t, because they don’t know the dive-specific protocols. You want a physician trained in dive medicine specifically.

Where to find one:

• DAN’s physician referral list — diversalertnetwork.org maintains a global directory of dive-trained doctors
• UHMS member directory — undersea and hyperbaric specialists, many of whom do dive medicals
• SPUMS in Australia / New Zealand, EUBS in Europe
• Your local dive shop almost certainly knows the nearest dive doc, because they refer borderline cases regularly

Expect a dive medical to take 30–60 minutes and cost roughly $80–200 / £80–150 / 800–1,500 SEK depending on country. You’ll bring your HbA1c results, complications screening, hypoglycemia history, and medication list. They’ll sign a fit-to-dive form (or not). Bring it to the dive shop. Done.

The shops will not usually ask to see your medical unless something flags on the standard medical questionnaire (the RSTC / WRSTC form), where Yes answers to diabetes-related questions trigger the requirement for a physician’s note. Lying on that form is a really bad idea — your dive insurance can void the moment something goes wrong if you concealed a relevant condition.

A practical reality check

A well-managed Type 2 diabetic on metformin, with a clean complications screen and an HbA1c of 6.5%, can typically get cleared for diving with no fuss. A Type 1 diabetic with a CGM, no severe hypos in years, and a good endocrinologist often gets cleared too — but the dive day routine is more demanding.

Diving with diabetes adds friction. More planning, more snacks, more checks, slightly less spontaneity. None of it is heroic. Hundreds of thousands of diabetics dive recreationally worldwide. The protocols work.

What does not work: deciding you’ll “be careful” without medical clearance, skipping pre-dive glucose checks because you feel fine, or trusting that a tropical resort divemaster will know what a glucagon kit is. Your safety underwater is your responsibility. The protocols exist because divers — diabetic and not — have died from the failures they prevent.

Ready to plan a diving trip with diabetes?

Talk to your endocrinologist and a DAN-listed dive physician first. Once you’re cleared, Koh Tao is a forgiving place to start — warm water, short boat rides, shallow training dives, plenty of shops used to handling medical paperwork. Pick a shop with small group sizes, brief the instructor properly, and the rest is just diving.